Image-forming lens, and camera device and portable information terminal device with the image-forming lens

ABSTRACT

An image forming lens consists of from an object side to an image side in the following order: a first group with a positive refractive power; an aperture stop; and a second group with a positive refractive power, wherein the second group includes, from the object side to the image side in the following order, a biconvex lens, a biconcave lens, a negative meniscus lens a convex surface of which faces the image side, a biconvex lens, and a positive meniscus lens a convex surface of which faces the image side.

CROSS REFERENCE RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/030,623, filed Sep. 18, 2013, which is a continuation of U.S.application Ser. No. 13/803,262 (now U.S. Pat. No. 8,547,651), filedMar. 14, 2013, which is a divisional application of U.S. applicationSer. No. 13/162,025 (now U.S. Pat. No. 8,526,128), filed on Jun. 16,2011 and is based on and claims priority from Japanese patentapplication numbers 2010-137482, filed Jun. 16, 2010, 2010-137492, filedJun. 16, 2010, and 2011-118460, filed May 26, 2011, the disclosures ofwhich are hereby incorporated by reference herein in their entireties.

BACKGROUND

The present invention relates to an image-forming lens, and to cameradevices such as a silver-halide camera, a digital camera, a videocamera, a surveillance camera, and the like and a portable informationterminal device with the image-forming lens.

In recent years, as an imaging apparatus using an image sensor such as aCCD, a CMOS, and the like, a digital still camera, and a digital videocamera have been widely used. In particular, as such an imagingapparatus, the digital still camera has been widely used to replace thesilver-halide camera.

In accordance with increasing the number of pixels on an image sensorused in such an imaging apparatus, further higher optical performance ofan image-forming lens as an imaging lens is required. In addition,miniaturization in consideration of portability of the imaging apparatushas also advanced, and in the market of imaging apparatuses, imagingapparatuses having high performance and miniaturization have becomemainstream. Not only high performance but also miniaturization of theimaging lens is required, too.

Moreover, since speeding up of a shooting speed has also advanced, abrighter lens as the imaging lens is required.

Regarding a field angle of the imaging lens for the digital camera, somedegree of wide angle used for easily taking a snapshot is preferred, anda half-field angle: 38 degrees corresponding to a focal lengthcorresponding to 28 mm on a 35 mm photography basis is one of guides ofthe field angle.

In a known imaging lens of a retrofocus type as a typical example of awide-angle lens having a single focus, a front lens group has a negativerefractive power, and it is possible to distance an exit pupil positionfrom an image plane. However, a principle point is in the rear of theentire lens system, and therefore asymmetry of the refractive powerarrangement increases, and corrections of comatic aberration,distortion, and transverse chromatic aberration may be incomplete.Imaging lenses of the retrofocus type are disclosed in Japanese patentnumbers 2942280 and 2991524, and various types other than the above areknown.

Additionally, an imaging lens in which a front lens group has a positiverefractive power and the field angle is wide is disclosed in Japanesepatent application publication number 2006-349920, Japanese patentnumber 3392964, and so on.

An image-forming lens disclosed in Japanese patent number 2942280 is atwo lens-group type having negative and positive lens groups, and in thespecifically-described embodiment, an entire length of the lens is long,and there is about −3% of distortion. An image-forming lens disclosed inJapanese patent number 2991524 is also a two lens-group type havingnegative and positive lens groups, and has a small number of lenselements. However, the entire length of the lens is long, and therestill is room for improvement in terms of correction of field curvature.

An image-forming lens disclosed in Japanese patent applicationpublication number 2006-349920 is a two lens-group type having apositive-lens group as a front lens group, and small, and in whichaberration is suitably corrected. However, a color difference of comaticaberration is not well-considered.

An image-forming lens disclosed in Japanese patent number 3392964 isalso a two lens-group type having a positive-lens group as a front lensgroup, and in the specifically-described embodiment, there is about −10%of distortion, and there still is room for improvement in terms ofcorrection of aberration.

Incidentally, in an imaging apparatus where an image sensor images animage formed by the image-forming lens, the number of pixels on theimage sensor has increased in recent years, and the use of the imagesensor having a large number of pixels which are equal to or more than10 million pixels has spread.

When an arrangement pitch of the pixels on this image sensor isenlarged, light sensitivity of the image sensor becomes higher, and thedepth of field with regard to an imaged image becomes shallower, and anadvantage in a shooting condition is large.

However, in a case where an image sensor is used on which an arrangementpitch of the pixels is large and the size of an imaging plane is large,as an image-forming lens which forms a shot image on an image sensor,generally, an image-forming lens in which an entire optical length (adistance between a lens surface on a most object side of theimage-forming lens and the imaging plane) is long and a lens diameter islarge is needed, and therefore the size of the imaging apparatus becomeslarge and portability becomes poor.

On the other hand, in order to make smaller the size of the imagingapparatus, when the image-forming lens is closer to a large-sizedimaging plane, a field angle of an incident light flux onto the imagingplane increases, and there is a possibility of becoming difficult tocorrect aberration.

SUMMARY

An object of the present inventions is to provide an image-forming lenssystem which is small and provides good performance, and a camera deviceand a portable information terminal device using the image-forming lenssystem as an imaging lens.

In order to achieve the above object, an embodiment of the presentinvention provides: an image-forming lens comprising: from an objectside to an image side in order, a first group with a positive refractivepower which includes less than or equal to five lens elements of twonegative lenses and equal to or more than two positive lenses and inwhich a first lens element on a most object side is a negative meniscuslens a convex surface of which faces the object side; an aperture; and asecond group with a positive refractive power which includes less thanor equal to five lens elements including at least one cemented lens of apositive lens and a negative lens; wherein each of the first group andthe second group shifts independently to perform focusing to a limitedobject distance, and an interval between the first lens element and asecond lens element placed close to a surface on the image side of thefirst lens element: d1₁₋₂ and an interval between the second lenselement and a third lens element placed close to a surface on the imageside of the second lens element: d1₂₋₃ satisfy Conditional Expression A:0.0<d1₂₋₃/d1₁₋₂<1.0.

In order to achieve the above object, an embodiment of the presentinvention provides: an image-forming lens comprising: from an objectside to an image side in order, a first group with a positive refractivepower which includes less than or equal to four lens elements of equalto or more than two negative lenses and one positive lens and in which afirst lens element on a most object side is a negative meniscus lens aconvex surface of which faces the object side and a second lens elementplaced close to a surface on the image side of the first lens element isa negative lens; an aperture; and a second group with a positiverefractive power which includes five lens elements including at leastone cemented lens of a positive lens and a negative lens; wherein eachof the first group and the second group shifts independently to performfocusing to a limited object distance, and an interval between the firstlens element and the second lens element: d1₁₋₂ and an interval betweenthe second lens element and a third lens element placed close to asurface on the image side of the second lens element: d1₂₋₃ satisfyConditional Expression B: 0.0<d1₂₋₃/d1₁₋₂<0.4.

In order to achieve the above object, an embodiment of the presentinvention provides: an image-forming lens comprising: from an objectside to an image side in order, a first group with a positive refractivepower which includes less than or equal to five lens elements of twonegative lenses and equal to or more than two positive lenses and inwhich a first lens element on a most object side is a negative meniscuslens a convex surface of which faces the object side; an aperture; and asecond group with a positive refractive power which includes less thanor equal to five lens elements including at least one cemented lens of apositive lens and a negative lens, a negative lens and a positive lens;wherein each of the first group and the second group shiftsindependently to perform focusing to a limited object distance, and aninterval between the first lens element and a second lens element placedclose to a surface on the image side of the first lens element: d1₁₋₂and an interval between the second lens element and a third lens elementplaced close to a surface on the image side of the second lens element:d1₂₋₃ satisfy Conditional Expression A: 0.0<d1₂₋₃/d1₁₋₂<1.0.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a lens constitution of an image-forminglens of Example 1.

FIG. 2 is an aberration diagram of the image-forming lens of Example 1.

FIG. 3 is a diagram illustrating a lens constitution of an image-forminglens of Example 2.

FIG. 4 is an aberration diagram of the image-forming lens of Example 2.

FIG. 5 is a diagram illustrating a lens constitution of an image-forminglens of Example 3.

FIG. 6 is an aberration diagram of the image-forming lens of Example 3.

FIG. 7 is a diagram illustrating a lens constitution of an image-forminglens of Example 4.

FIG. 8 is an aberration diagram of the image-forming lens of Example 4.

FIG. 9 is a diagram illustrating a lens constitution of an image-forminglens of Example 5.

FIG. 10 is an aberration diagram of the image-forming lens of Example 5.

FIG. 11 is a diagram illustrating a lens constitution of animage-forming lens of Example 6.

FIG. 12 is an aberration diagram of the image-forming lens of Example 6.

FIG. 13 is a diagram illustrating a lens constitution of animage-forming lens of Example 7.

FIG. 14 is an aberration diagram of the image-forming lens of Example 7.

FIG. 15 is a diagram illustrating a lens constitution of animage-forming lens of Example 8.

FIG. 16 is an aberration diagram of the image-forming lens of Example 8.

FIG. 17 is a diagram illustrating a lens constitution of animage-forming lens of Example 9.

FIG. 18 is an aberration diagram of the image-forming lens of Example 9.

FIG. 19 is a diagram illustrating a lens constitution of animage-forming lens of Example 10.

FIG. 20 is an aberration diagram of the image-forming lens of Example10.

FIG. 21 is a diagram illustrating a lens constitution of animage-forming lens of Example 11.

FIG. 22 is an aberration diagram of the image-forming lens of Example11.

FIG. 23 is a diagram illustrating a lens constitution of animage-forming lens of Example 12.

FIG. 24 is an aberration diagram of the image-forming lens of Example12.

FIG. 25 is a diagram illustrating a lens constitution of animage-forming lens of Example 13.

FIG. 26 is an aberration diagram of the image-forming lens of Example13.

FIG. 27 is a diagram illustrating a lens constitution of animage-forming lens of Example 14.

FIG. 28 is an aberration diagram of the image-forming lens of Example14.

FIG. 29 is a diagram illustrating a lens constitution of animage-forming lens of Example 15.

FIG. 30 is an aberration diagram of the image-forming lens of Example15.

FIG. 31 is a diagram illustrating a lens constitution of animage-forming lens of Example 16.

FIG. 32 is an aberration diagram of the image-forming lens of Example16.

FIG. 33 is a diagram illustrating a lens constitution of an imageforming lens of Example 17.

FIG. 34 is an aberration diagram of the image-forming lens of Example17.

FIG. 35A to 35C are diagrams illustrating an example of an embodiment ofa portable information terminal device.

FIG. 36 is a system diagram of the portable information terminal device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In an image-forming lens according to an example of the presentinvention, a first group and a second group are shifted independently,and an interval between the first group and the second group is changedby focusing depending on an object distance, in a case of focusing on anobject in a limited object distance.

Conditional Expression B: 0.0<d1₂₋₃/d1₁₋₂<0.4 is a conditionalexpression in which a change of an interval between lens elements inaccordance with focusing is considered. In a case where ConditionalExpression B is not satisfied, axial chromatic aberration occurring bythe change of the interval between the lens elements tends to becorrected excessively, and comatic aberration easily occurs greatly. InConditional Expression B, d1₁₋₂ denotes an interval between a first lenselement and a second lens element placed on an image side of the firstlens element, and d1₂₋₃ denotes an interval between the second lenselement and a third lens element placed on an image side of the secondlens element.

Conditional Expression C: 1.2<|f1₁/F|<1.8 is a conditional expression tocontrol a range of magnitude relationship between a focal length f1₁(<0) of a negative meniscus lens (a first lens element) placed on a mostobject side of the first group and a focal length F (>0) of an entirelens system. The image-forming lens according to an example of thepresent invention enables a large diameter by placing a negativemeniscus lens a convex surface of which faces an object side on the mostobject of the first group. And in a case where Conditional Expression Cis not satisfied, a refractive power of the first lens element (negativemeniscus lens) is larger or smaller with respect to a refractive powerof the entire lens system, and an incident angle of an incident lightflux is greatly affected, and comatic aberration becomes large.

Under the condition of a large diameter, beyond a range of ConditionalExpression D: −0.7<R1₂/R1₃≦0.0, an incident angle of an incident lightflux is greatly affected, and spherical aberration and comaticaberration occur greatly. In Conditional Expression D, R1₂ denotes aradius of curvature on the image side of the first lens element, and R1₃denotes a radius of curvature on the object side of the second lenselement.

Conditional Expression E: 0.7<f1_(n1)/f1_(n12)<2.3 is a conditionalexpression to control a range of magnitude relationship of the ratiobetween a focal length of the first lens element and a combined focallength of the first lens element and a second lens element next on animage side of the first lens element. In Conditional Expression E,f1_(n1) denotes a focal length of the first lens element, and f1_(n12)denotes a combined focal length of the first lens element and the secondlens element.

In a case where Conditional Expression E is not satisfied, refractivepower balance between the first lens element and the second lens elementcollapses, axial chromatic aberration is corrected excessively, andadditionally, an angle of an incident light flux is greatly changed, andcomatic aberration increases.

Conditional Expression F: 30<Nd3·νd3−Nd4·νd4<50 is a conditionalexpression to correct axial chromatic aberration favorably. By forming alens element on the most image side of the first group into a cementedlens of a positive lens and a negative lens, it is possible for thecemented lens to have a function of correcting axial chromaticaberration. However, in a case where Conditional Expression F is notsatisfied, axial chromatic aberration is corrected excessively. InConditional Expression F, Nd3 denotes a refractive index of a d-line ofthe positive lens, νd3 denotes an Abbe's number of the d-line of thepositive lens, Nd4 denotes a refractive index of a d-line of thenegative lens, and νd4 denotes an Abbe's number of the d-line of thepositive lens.

In later-described examples where the cemented lens of the positive lensand the negative lens is used in the first group, ahigh-refractive-index and low-dispersion glass of the refractive indexof the d-line Nd3=equal to more than 1.8, and Abbe's number of thed-line νd3≈about 40 is used as the positive lens, and ahigh-refractive-index and high-dispersion glass of the refractive indexof the d-line Nd4=equal to more than 1.8, and Abbe's number of thed-line νd4=about 23 is used as the negative lens, and thereby axialchromatic aberration is optimized.

The image-forming lens according to an example of the present inventionpreferably has a positive lens of the first group that is a biconvexlens, and a lens element on the most image side of the second group thatis a biconvex lens. A lens element on the image side of the first groupcan be a single biconvex lens, and also can be structured by a biconvexlens and a concave lens placed on an image side of the biconvex lens. Ina case where the concave lens is placed on the image side of thebiconvex lens, the biconvex lens and the concave lens can be a cementedlens.

In addition, in a case where the lens element on the most object side ofthe second group is a biconvex lens, a negative lens can be cemented onan image side of the biconvex lens.

Conditional Expression G: 0.9<f1_(ep)/f2₁₁<2.2 is a conditionalexpression to control magnitude relationship of power of the biconvexlenses, in a case where each of these biconvex lenses is usedindividually, or in a case where these biconvex lenses are used ascemented lenses. In Conditional Expression G, f1_(ep) denotes a focallength of the positive lens of the first group, and f2₁₁ denotes a focallength of the most object side of the second group.

Preferably, in the image-forming lens according to an example of thepresent invention, the first lens element and the second lens elementare negative lenses, positions of a lens element on a most image side ofthe first group and a lens element on a most object side of the secondgroup are parts where light flux is largest. Magnitude relationship oflight flux in these parts is greatly affected on spherical aberration.In a case where Conditional Expression G is not satisfied, balance ofspherical aberration collapses, and image-forming performance in thecenter of the image plane is affected.

Conditional Expression H: 0.5<|R1₁/R2_(e)|<1.5 is a conditionalexpression which relates to a correction of astigmatism, comaticaberration, and spherical aberration. When Condition Expression Hexceeds a lower limit, astigmatism increases, and excessive comaticaberration occurs, and the entire optical length becomes long. InConditional Expression H, R1₁ denotes a radius of curvature of a surfaceon an object side of the first lens element, and R2_(e) denotes a radiusof curvature of a surface on an image side of a lens element on a mostimage side of the second group.

When Condition Expression H exceeds an upper limit, negative sphericalaberration occurs greatly, and astigmatism increases, and imageperformance is greatly affected.

Conditional Expression I: 1.4<|R1_(e)/R2₁|<34.0 is a conditionalexpression which relates to a correction of distortion and astigmatism.In a case where Conditional Expression I is not satisfied, negativedistortion or positive distortion occurs greatly, and astigmatism alsoincreases excessively.

A lens surface on a most image side of the first group and a lenssurface on a most object side of the second group have convex shapes,preferably. That is, it is possible to suppress the occurrence oftransverse chromatic aberration, astigmatism, and distortion by forminglens surfaces next to each other via the aperture interposed between thefirst group and the second group into an approximately symmetric shape.

As described in later-described Examples, by satisfying theabove-described Conditional Expressions B to I, it is possible toachieve an image-forming lens which is bright, and small, and providesgood performance.

An image-forming lens according to an example of the present inventionperforms focusing to the limited object distance by shiftingindependently each of the first group and the second group. ConditionalExpression J: −1.0<Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|<−0.4 is aconditional expression that relates to focusing to such a limited objectdistance. In Conditional Expression J, |(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|expresses a ratio between a shifting amount of the first group and ashifting amount of the second group of a case of focusing to an objectin infinity and a case of focusing to a reference closest imagingdistance. If |(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))| is “0(D1_(∞)=D1_(t))”,the shift amounts of the first group and the second group are the same,and the image-forming lens integrally shifts to the object side toperform focusing. In Conditional Expression J, D1_(∞) denotes aninterval between the first group and the second group in a case where anobject position is infinity, D1_(t) denotes an interval between thefirst group and the second group in a case of focusing to a referenceclosest imaging distance, D2_(∞) denotes an interval between the secondgroup and an image plane in a case where the object position isinfinity, and D2_(t) denotes an interval between the second group andthe image plane in a case of focusing to the reference closest imagingdistance. And Log is taken as a common logarithm.

When Conditional Expression J exceeds a lower limit, the shift amount ofthe first group decreases, and an influence of a production error ofeach group increases. Therefore, a highly accurate assembly operation isrequired in a case of assembling the lens, and accordingly it isunfavorable in terms of production cost.

In addition, in a case of focusing on an object position more distantthan the reference closest imaging distance, it is not easy to shift thefirst group by a small accurate shift amount.

When Conditional Expression J exceeds an upper limit, shift amounts ofthe first group and the second group for focusing increase.

When the shift amount for focusing increases, operability andportability of a camera device and a portable information terminaldevice are easily damaged. Additionally, it is not easy to achievehigh-speed focusing which is necessary for high-speed imaging.

As described above, in the image-forming lens according to an example ofthe present invention, in a case of focusing on an object in the limitedobject distance, each of the first group and the second group shiftsindependently, and an interval between the first group and the secondgroup is changed by focusing depending on the object distance.

Conditional Expression A: 0.0<d1₂₋₃/d1₁₋₂<1.0 is a conditionalexpression to correct properly axial chromatic aberration by a change ofthe interval of lens elements in accordance with such focusing andsuppress an occurrence of comatic aberration. In a case whereConditional Expression A is not satisfied, the axial chromaticaberration occurring by the change of the interval of the lens groupstends to be corrected excessively, and comatic aberration also occursgreatly. In Conditional Expression A, d1₁₋₂ denotes an interval betweenthe first lens element and a second lens element placed on an image sideof the first lens element, and d1₂₋₃ denotes an interval between thesecond lens element and a third lens element placed on an image side ofthe second lens element.

Conditional Expression K: −0.1<f1₁/f1₂<−1.0 is a conditional expressionrelates to correction of spherical aberration, astigmatism, and fieldcurvature. In a case where Conditional Expression K is not satisfied,power balance between a negative meniscus lens (first lens element) on amost object side of the first group a convex surface of which faces theobject side and a positive lens (a second lens element) next to asurface on an image side of the negative meniscus lens collapses, andbalance between spherical aberration and astigmatism becomes worse, andfield curvature occurs greatly. The image-forming lens according to anexample of the present invention is capable of being a large diameter byplacing the negative meniscus lens the convex surface of which faces theobject side on the most object side of the first group. In a case whereConditional Expression K is not satisfied, influence on the incidentlight flux increases. In Conditional expression K, f1₁ denotes a focallength of the first lens element, and f1₂ denotes a focal length of thesecond lens element.

Conditional Expression L: 0.4<|R1₁/R2_(e)|<2.1 is a conditionalexpression that relates to correction of astigmatism, comaticaberration, and spherical aberration. When Conditional Expression Lexceeds a lower limit, excessive astigmatism and comatic aberrationoccur. When Conditional Expression L exceeds an upper limit, negativespherical aberration increases, and excessive astigmatism occurs. InConditional Expression L, R1₁ denotes a radius of curvature of a surfaceon an object side of the first lens element, and R2_(e) denotes a radiusof curvature of a surface on an image side of a lens element on a mostobject side of the second group.

Conditional Expression M: 1.2<|R1_(e)/R2₁|<2.6 is a conditionalexpression that relates to correction of distortion, and astigmatism. Ina case where Conditional Expression M is not satisfied, positivedistortion or negative distortion increases, and astigmatism alsobecomes excessive. In Conditional Expression M, R1_(e) denotes a radiusof curvature of a surface on an object side of the first lens element,and R2₁ denotes a radius of curvature of a surface on an image side of alens element on a most object side of the second group.

The image-forming lens according to an example of the present inventionperforms focusing to the limited object distance by shiftingindependently each of the first group and the second group. ConditionalExpression N: −1.5E+1<Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|<−5.0E−2 is aconditional expression that relates to focusing to such a limited objectdistance. In Conditional Expression N, |(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|expresses a ratio between a shift amount (an extension amount) of thefirst group and a shift amount (an extension amount) of the second groupof a case of focusing to an object in infinity and a case of focusing tothe reference closest imaging distance. If|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))| is “0(D1_(∞)−D1_(t))”, the shiftamounts of the first group and the second group are the same, and theimage-forming lens integrally shifts to the object side to performfocusing. In Conditional Expression N, D1_(∞) denotes an intervalbetween the first group and the second group in a case where an objectposition is infinity, D1_(t) denotes an interval between the first groupand the second group in a case of focusing to a reference closestimaging distance, D2_(∞) denotes an interval between the second groupand an image plane in a case where the object position is infinity, andD2_(t) denotes an interval between the second group and the image planein a case of focusing to the reference closest imaging distance. And Logis taken as a common logarithm.

When Conditional Expression N exceeds a lower limit, the shift amount ofthe first group decreases, an influence of a production error of eachgroup increases. Therefore, a highly accurate assembly operation isrequired in a case of assembling the lens, and accordingly it isunfavorable in terms of production cost.

In addition, in a case of focusing on an object position more distantthan the reference closest imaging distance, it is not easy to shift thefirst group by a small accurate shift amount.

When Conditional Expression N exceeds an upper limit, shift amounts ofthe first group and the second group for focusing increase.

When the shift amount for focusing increases, operability andportability of a camera device and a portable information terminaldevice are easily damaged. Additionally, it is not easy to achievehigh-speed focusing which is necessary for high-speed imaging.

It is possible to correct chromatic aberration by forming each of a lenselement on a most image side of the first group and a lens element on amost object side of the second group into a cemented lens of a positivelens and a negative lens. Additionally, using a cemented lens makesassembly of the lens easy in a case of actual assembling of theimage-forming lens.

In particular, by using the cemented lens as the lens element on themost object side of the second group, it is possible to correct axialchromatic aberration effectively.

Conditional Expression O: 2.0<f1_(e)/f2₁<7.9 is a conditional expressionthat relates to correction of spherical aberration and astigmatism bycontrolling each power balance between the cemented lens on the mostimage side of the first group and the cemented lens on the most objectside of the second group. When Conditional Expression O exceeds a lowerlimit, astigmatism increases by lack of correction of sphericalaberration. When Conditional Expression O exceeds an upper limit,astigmatism increases. In Conditional Expression O, f1_(e) denotes afocal length of the first cemented lens, and f2₁ denotes a focal lengthof the second cemented lens.

Conditional Expression P: 0.7<(Nd4·νd4−Nd3·νd3)/(Nd5·νd5−Nd6·νd6)<1.6 isa conditional expression to control a combination of materials of acemented lens in a case of forming a lens element on a most image sideof the first group into a cemented lens of a positive lens and anegative lens and forming a lens element on a most object side of thesecond group into a cemented lens of a positive lens and a negativelens. In a case where Conditional Expression P is satisfied, it ispossible to correct favorably axial chromatic aberration and astigmatismin particular. However, in a case where Conditional Expression P is notsatisfied, axial chromatic aberration and astigmatism increase. InConditional Expression P, Nd3 denotes a refractive index of a d-line ofthe negative lens of the first cemented lens, νd3 denotes an Abbe'snumber of the d-line of the negative lens of the first cemented lens,Nd4 denotes a refractive index of a d-line of the positive lens of thefirst cemented lens, νd4 denotes an Abbe's number of the d-line of thepositive lens of the first cemented lens, Nd5 denotes a refractive indexof a d-line of the positive lens of the second cemented lens, νd5denotes an Abbe's number of the d-line of the positive lens of thesecond cemented lens, Nd6 denotes a refractive index of a d-line of thenegative lens of the second cemented lens, and νd6 denotes an Abbe'snumber of the d-line of the negative lens of the second cemented lens.

As described in the examples, by satisfying Conditional Expressions A,K, and L to N, it is possible to achieve a bright and smallimage-forming lens that provides good performance. In addition, bysatisfying Conditional Expressions O and P, it is possible to achievefavorable performance.

An arrangement position of an aperture can be between the first groupand the image plane, however from the viewpoint that it is possible tosuppress an occurrence of pupil aberration, prevent lens diameters ofthe first group and the second group from increasing excessively in sizeby the a front aperture or a rear aperture, miniaturize, and so on, amost favorable arrangement position of the aperture is between the firstgroup and the second group.

As described above, the first group includes less than or equal to fivelens elements including two negative lenses and equal to or more thantwo positive lenses. A lens element (a first lens element) on a mostobject side is a negative meniscus lens a convex surface of which facesthe object side, and a lens element (a second lens element) next to animage side of the negative meniscus lens is a positive lens.

In such a lens constitution, aberrations occurring in the negative lenson the most object side (the negative meniscus lens the convex surfaceof which faces the object side, the first lens element), sphericalaberration and astigmatism in particular, are corrected by the positivelens next to the surface on the image side of the negative lens (thesecond lens element), and by using other positive lens and negativelens, it is possible to correct axial chromatic aberration.

Preferably, the second group includes less than or equal to five lenselements including at least one cemented lens of a positive lens and anegative lens, a negative lens, and a positive lens. Therefore, in thiscase, the second group includes four or five lens elements.

Thus, in the second group, other than the at least one cemented lens,equal to or more than two lens elements are used. By constituting thesecond group as the above, it is possible to effectively correct comaticflare, astigmatism, and field curvature.

In addition, preferably, by forming each of a shape of a lens surface onthe most image side of the first group and a shape of a lens surface onthe most object side of the second group into a convex shape,respectively, and placing the aperture between the first group and thesecond group, a shape of the lens surfaces next to each other via theaperture interposed between the first group and the second group becomesapproximately symmetric, and therefore it is possible to effectivelysuppress an occurrence of transverse chromatic aberration, astigmatism,and distortion in particular.

Moreover, preferably, the first group of the image-forming lensaccording to an example of the present invention includes less than orequal to four lens elements including equal to or more than two negativelenses and one positive lens. In particular, the first group includesthree lens elements of two negative lenses and one positive lens, orincludes four lens elements of three negative lenses and one positivelens.

Preferably, two lens elements from the most object side of the firstgroup are negative lenses, and a negative lens on the most object side(a first lens element) is a negative meniscus lens a convex surface ofwhich faces the object side. A negative lens (a second lens element)placed on an image side of the negative meniscus lens on the most objectside can be a negative meniscus lens, or a plano-concave lens, orbiconcave lens, as described in later-described examples.

In a case where two negative meniscus lenses are placed from the mostobject side of the first group, it is preferable that concave surfacesof these negative meniscus lenses face each other.

In a case where the first group includes three lens elements, a positivelens is placed on the most image side. The positive lens is a biconvexlens, preferably.

In a case where the first group includes four lens elements, it ispreferable to place a negative lens and a positive lens in order fromthe most image side of the first group, and the positive lens and thenegative lens can be a cemented lens. In each case, it is preferablethat the positive lens be a biconvex lens and the negative lens be anegative meniscus lens.

As described above, in the image-forming lens according to a example ofthe present invention, two negative lenses are placed from the mostobject side of the first group. By successively placing two negativelenses in this manner, it is possible to favorably correct transversechromatic aberration and comatic aberration in particular.

Additionally, it is possible to achieve a large diameter by a negativemeniscus lens on the most object side a convex surface of which facesthe object side.

In the second group, at least one cemented lens of a positive lens and anegative lens is included. By this cemented lens, it is possible tofavorably correct axial chromatic aberration. Since five lens elementsconstitute the second group, three lens elements other than the cementedlens can be used. By those lens elements, it is possible to effectivelycorrect comatic flare, astigmatism, and field curvature.

In later-described examples, including a purpose of ensuring a backfocus, the second group includes a combination of a cemented lens, anegative lens, a positive lens, and a positive lens, from the objectside in order. However, other than the above combination, for example,by using three lens elements other than the cemented lens, it ispossible to correct various aberrations, and the lens constitution ofthe second group is not limited thereto.

As described above, the image-forming lens according to an example ofthe present invention has two positive and positive groups, and thenumber of lens elements are eight to ten.

Hereinafter, embodiments of the present invention will be explained.

FIGS. 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, and 33illustrate embodiments of an image-forming lens. The embodimentsillustrated in those drawings illustrate an arrangement of lens elementsin a case where an object distance of the image-forming lens isinfinity.

Each of those embodiments respectively corresponds to Examples 1 to 17described later in order.

In FIGS. 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, and33 reference signs are shared. A lens element, which is in the ith fromthe left in the drawings which is an object side, has a reference signLi (i=1 to 10), and “Stop” denotes an aperture. A transparent parallelplate arranged on an image plane side of a lens system illustrates acover glass of an image sensor, various filters, or the like as anoptically equivalent transparent parallel plate.

As a digital still camera, in a camera device using a CCD (CMOS) imagesensor, between an image-forming lens system and an image sensor, atleast one of a back glass, a low-pass filter, an infrared cut glass, acover glass for protecting a light-receiving surface of a CCD (CMOS)image sensor, and the like is interposed. Such an inserted transparentplate is illustrated as one transparent parallel plate as illustratedabove.

Each surface of the lens elements, the aperture “Stop”, and thetransparent parallel plate has a serial number (1, 2, 3 . . . ) as asurface number.

In an embodiment illustrated in FIG. 1, an image-forming lens includesnine lens elements L1 to L9. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 1) constitute a first group, and lens elements L5 to L9arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 1) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a negative meniscuslens a convex surface of which faces the image side. The lens element L3is a biconvex lens. The lens element L4 is a negative meniscus lens aconvex surface of which faces the image side. The lens element L3 andthe lens element L4 are cemented.

The lens element L5 is a biconvex lens. The lens element L6 is abiconcave lens. The lens element L7 is a negative meniscus lens. Thelens element L8 is a positive meniscus lens. The lens element L9 is apositive meniscus lens a convex surface of which faces the image side.The lens element L5 and the lens element L6 are cemented. And the lenselement L7 and the lens element L8 are also cemented.

In an embodiment illustrated in FIG. 3, an image-forming lens includesnine lens elements L1 to L9. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 3) constitute a first group, and lens elements L5 to L9arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 3) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a plano-concave lensa surface on the image side of which is flat. The lens element L3 is abiconvex lens. The lens element L4 is a negative meniscus lens a convexsurface of which faces the image side. The lens element L3 and the lenselement L4 are cemented.

The lens element L5 is a biconvex lens. The lens element L6 is abiconcave lens. The lens element L7 is a biconcave lens. The lenselement L8 is a biconvex lens. The lens element L9 is a positivemeniscus lens a convex surface of which faces the image side. The lenselement L5 and the lens element L6 are cemented. And the lens element L7and the lens element L8 are also cemented.

In an embodiment illustrated in FIG. 5, an image-forming lens includeseight lens elements L1 to L8. Lens elements L1 to L3 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 5) constitute a first group, and lens elements L4 to L8arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 5) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a plano-concave lensa surface on the object side of which is flat. The lens element L3 is abiconvex lens.

The lens element L4 is a biconvex lens. The lens element L5 is abiconcave lens. The lens element L6 is a biconcave lens. The lenselement L7 is a biconvex lens. The lens element L8 is a positivemeniscus lens a convex surface of which faces the image side.

The lens element L4 and the lens element L5 are cemented, and the lenselement L6 and the lens element L7 are also cemented.

In an embodiment illustrated in FIG. 7, an image-forming lens includeseight lens elements L1 to L8. Lens elements L1 to L3 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 7) constitute a first group, and lens elements L4 to L8arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 7) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a negative meniscuslens a convex surface of which faces the image side. The lens element L3is a biconvex lens.

The lens element L4 is a biconvex lens. The lens element L5 is abiconcave lens. The lens element L6 is a negative meniscus lens aconcave surface of which faces the object side. The lens element L7 is apositive meniscus lens a convex surface of which faces the image side.The lens element L8 is a positive meniscus lens a convex surface ofwhich faces the image side.

The lens element L4 and the lens element L5 are cemented, and the lenselement L6 and the lens element L7 are also cemented.

In an embodiment illustrated in FIG. 9, an image-forming lens includesnine lens elements L1 to L9. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 9) constitute a first group, and lens elements L5 to L9arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 9) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a negative meniscuslens a convex surface of which faces the image side. The lens element L3is a biconvex lens. The lens element L4 is a negative meniscus lens aconvex surface of which faces the image side.

The lens element L3 and the lens element L4 are cemented.

The lens element L5 is a biconvex lens. The lens element L6 is abiconcave lens. The lens element L7 is a negative meniscus lens a convexsurface of which faces the image side. The lens element L8 is a biconvexlens. The lens element L9 is a positive meniscus lens a convex surfaceof which faces the image side. The lens element L5 and the lens elementL6 are cemented.

In an embodiment illustrated in FIG. 11, an image-forming lens includesnine lens elements L1 to L9. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 11) constitute a first group, and lens elements L5 to L9arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 11) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a negative meniscuslens a convex surface of which faces the image side. The lens element L3is a biconvex lens. The lens element L4 is a negative meniscus lens aconvex surface of which faces the image side. The lens element L4 isclose to a surface on the image side of the lens element L3, but is notcemented to the lens element L3.

The lens element L5 is a biconvex lens. The lens element L6 is abiconcave lens. The lens element L7 is a biconcave lens. The lenselement L8 is a biconvex lens. The lens element L9 is a positivemeniscus lens a convex surface of which faces the image side. The lenselement L7 and the lens element L8 are cemented.

In an embodiment illustrated in FIG. 13, an image-forming lens includesnine lens elements L1 to L9. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 13) constitute a first group, and lens elements L5 to L9arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 13) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a negative meniscuslens, a convex surface of which faces the image side. The lens elementL3 is a biconvex lens. The lens element L4 is a negative meniscus lens aconvex surface of which faces the image side. The lens element L4 isclose to a surface on the image side of the lens element L3, but is notcemented to the lens element L3.

The lens element L5 is a biconvex lens. The lens element L6 is abiconcave lens. The lens element L7 is a biconcave lens. The lenselement L8 is a biconvex lens. The lens element L9 is a positivemeniscus lens a convex surface of which faces the image side. The lenselement L5 and the lens element L6 are cemented, and the lens element L7and the lens element L8 are also cemented.

In an embodiment illustrated in FIG. 15, an image-forming lens includesnine lens elements L1 to L9. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 15) constitute a first group, and lens elements L5 to L9arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 15) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a biconcave lens.The lens element L3 is a biconvex lens. The lens element L4 is anegative meniscus lens a convex surface of which faces the image side.The lens element L3 and the lens element L4 are cemented.

The lens element L5 is a biconvex lens. The lens element L6 is abiconcave lens. The lens element L7 is a negative meniscus lens a convexsurface of which faces the image side. The lens element L8 is a positivemeniscus lens a convex surface of which faces the image side. The lenselement L9 is a positive meniscus lens a convex surface of which facesthe image side. The lens element L5 and the lens element L6 arecemented.

In an embodiment illustrated in FIG. 17, an image-forming lens includesnine lens elements L1 to L9. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 17) constitute a first group, and lens elements L5 to L9arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 17) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a biconcave lens.The lens element L3 is a biconvex lens. The lens element L4 is anegative meniscus lens a convex surface of which faces the image side.The lens element L3 and the lens element L4 are cemented.

The lens element L5 is a biconvex lens. The lens element L6 is abiconcave lens. The lens element L7 is a biconcave lens. The lenselement L8 is a biconvex lens. The lens element L9 is a positivemeniscus lens a convex surface of which faces the image side. The lenselement L5 and the lens element L6 are cemented, and the lens element L7and the lens element L8 are cemented.

In an embodiment illustrated in FIG. 19, an image-forming lens includeseight lens elements L1 to L8. Lens elements L1 to L3 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 19) constitute a first group, and lens elements L4 to L8arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 19) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a negative meniscuslens a convex surface of which faces the image side. The lens element L3is a biconvex lens.

The lens element L4 is a biconvex lens. The lens element L5 is abiconcave lens. The lens element L6 is a biconcave lens. The lenselement L7 is a biconvex lens. The lens element L8 is a positivemeniscus lens a convex surface of which faces the image side. The lenselement L4 and the lens element L5 are cemented, and the lens element L6and the lens element L7 are also cemented.

In each of the above-described image-forming lenses, the first grouphaving a positive refractive power, the aperture “Stop”, and the secondgroup having a positive refractive power are arranged from the objectside (the left side in each drawing) to the image side (the right sidein each drawing) in order.

The first group includes less than or equal to four lens elementsincluding equal to or more than two negative lenses and one positivelens. Both of the lens element L1 and the lens element L2 from the mostthe object side are negative lenses, and the lens element L1 on the mostobject side is a negative meniscus lens a convex surface of which facesthe object side.

The second group includes five lens elements including at least onecemented lens where a positive lens and a negative lens are cemented.

The image-forming lenses of those embodiments perform focusing to alimited object distance by shifting each of the first group and thesecond group to the object side by a different extension amount, andsatisfy Conditional Expressions B to J, as described in Examples 1 to 10later described.

In an embodiment illustrated in FIG. 21, an image-forming lens includesnine lens elements L1 to L9. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 21) constitute a first group, and lens elements L5 to L9arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 21) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a biconvex lens. Thelens element L3 is a biconcave lens (negative lens). The lens element L4is a biconvex lens (positive lens). The lens element L3 and the lenselement L4 are cemented.

The lens element L5 is a biconvex lens (positive lens). The lens elementL6 is a biconcave lens (negative lens). The lens element L7 is abiconcave lens (negative lens). The lens element L8 is a biconvex lens(positive lens). The lens element L9 is a positive meniscus lens aconvex surface of which faces the image side. The lens element L5 andthe lens element L6 are cemented. The lens element L7 and the lenselement L8 are cemented.

Focusing is performed by shifting independently each of the first groupincluding the lens elements L1 to L4 and the second lens group includingthe lens elements L5 to L9 to the object side.

In an embodiment illustrated in FIG. 23, an image-forming lens includeseight lens elements L1 to L8. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 23) constitute a first group, and lens elements L5 to L8arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 23) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a positive meniscuslens a convex surface of which faces the object side. The lens elementL3 is a biconcave lens (negative lens). The lens element L4 is abiconvex lens (positive lens). The lens element L3 and the lens elementL4 are cemented.

The lens element L5 is a biconvex lens (positive lens). The lens elementL6 is a biconcave lens (negative lens). The lens element L7 is anegative meniscus lens a concave surface of which faces the object side.The lens element L8 is a positive meniscus lens a convex surface ofwhich faces the image side. The lens element L5 and the lens element L6are cemented.

Focusing is performed by shifting independently each of the first groupincluding the lens elements L1 to L4 and the second lens group includingthe lens elements L5 to L8 to the object side.

In an embodiment illustrated in FIG. 25, an image-forming lens includeseight lens elements L1 to L8. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 25) constitute a first group, and lens elements L5 to L8arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 25) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a positive meniscuslens a convex surface of which faces the object side. The lens elementL3 is a biconcave lens (negative lens). The lens element L4 is abiconvex lens (positive lens). The lens element L3 and the lens elementL4 are cemented.

The lens element L5 is a biconvex lens (positive lens). The lens elementL6 is a biconcave lens (negative lens). The lens element L7 is anegative meniscus lens a concave surface of which faces the object side.The lens element L8 is a positive meniscus lens a convex surface ofwhich faces the image side. The lens element L5 and the lens element L6are cemented.

Focusing is performed by shifting independently each of the first groupincluding the lens elements L1 to L4 and the second lens group includingthe lens elements L5 to L8 to the object side.

In an embodiment illustrated in FIG. 27, an image-forming lens includesten lens elements L1 to L10. Lens elements L1 to L5 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 27) constitute a first group, and lens elements L6 to L10arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 27) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a positive meniscuslens a convex surface of which faces the object side. The lens elementL3 is a positive meniscus lens a convex surface of which faces the imageside. The lens element L4 is a biconcave lens (negative lens). The lenselement L5 is a biconvex lens (positive lens). The lens element L4 andthe lens element L5 are cemented.

The lens element L6 is a biconvex lens (positive lens). The lens elementL7 is a biconcave lens (negative lens). The lens element L8 is abiconcave lens (negative lens). The lens element L9 is a biconvex lens(positive lens). The lens element L10 is a positive meniscus lens, aconvex surface of which faces the image side. The lens element L6 andthe lens element L7 are cemented. The lens element L8 and the lenselement L9 are cemented.

Focusing is performed by shifting independently each of the first groupincluding the lens elements L1 to L5 and the second lens group includingthe lens elements L5 to L10 to the object side.

In an embodiment illustrated in FIG. 29, an image-forming lens includesten lens elements L1 to L10. Lens elements L1 to L5 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 29) constitute a first group, and lens elements L6 to L10arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 29) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a positive meniscuslens a convex surface of which faces the object side. The lens elementL3 is a positive meniscus lens a convex surface of which faces theobject side. The lens element L4 is a biconcave lens (negative lens).The lens element L4 is a biconvex lens (positive lens). The lens elementL4 and the lens element L5 are cemented.

The lens element L6 is a biconvex lens (positive lens). The lens elementL7 is a biconcave lens (negative lens). The lens element L8 is abiconcave lens (negative lens). The lens element L9 is a biconvex lens(positive lens). The lens element L10 is a positive meniscus lens aconvex surface of which faces the image side. The lens element L6 andthe lens element L7 are cemented. The lens element L8 and the lenselement L9 are cemented.

Focusing is performed by shifting independently each of the first groupincluding the lens elements L1 to L5 and the second lens group includingthe lens elements L5 to L10 to the object side.

In an embodiment illustrated in FIG. 31, an image-forming lens includeseight lens elements L1 to L8. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 31) constitute a first group, and lens elements L5 to L8arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 31) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a positive meniscuslens a convex surface of which faces the object side. The lens elementL3 is a biconcave lens. The lens element L4 is a biconvex lens.

The lens element L5 is a biconvex lens (positive lens). The lens elementL6 is a biconcave lens (negative lens). The lens element L7 is anegative meniscus lens a concave surface of which faces the object side.The lens element L8 is a biconvex lens. The lens element L5 and the lenselement L6 are cemented.

Focusing is performed by shifting independently each of the first groupincluding the lens elements L1 to L4 and the second lens group includingthe lens elements L5 to L8 to the object side.

In an embodiment illustrated in FIG. 33, an image-forming lens includeseight lens elements L1 to L8. Lens elements L1 to L4 arranged on anobject side from the aperture “Stop” (the left side from the aperture“Stop” in FIG. 33) constitute a first group, and lens elements L5 to L8arranged on an image side from the aperture “Stop” (the right side fromthe aperture “Stop” in FIG. 33) constitute a second group.

The lens element L1 is a negative meniscus lens a convex surface ofwhich faces the object side. The lens element L2 is a positive meniscuslens a convex surface of which faces the object side. The lens elementL3 is a biconcave lens. The lens element L4 is a biconvex lens.

The lens element L5 is a biconvex lens (positive lens). The lens elementL6 is a biconcave lens (negative lens). The lens element L7 is anegative meniscus lens a concave surface of which faces the object side.The lens element L8 is a biconvex lens. The lens element L5 and the lenselement L6 are cemented.

Focusing is performed by shifting independently each of the first groupincluding the lens elements L1 to L4 and the second lens group includingthe lens elements L5 to L8 to the object side.

In each of the above-described image-forming lenses, the first grouphaving a positive refractive power, the aperture “Stop”, and the secondgroup having a positive refractive power are arranged from the objectside (the left side in each drawing) to the image side (the right sidein each drawing) in order.

The first group includes less than or equal to five lens elementsincluding two negative lenses and equal to or more than two positivelenses. The lens element L1 on the most object side is a negativemeniscus lens a convex surface of which faces the object side. Thesecond group includes less than or equal to five lens elements includingat least one cemented lens where a positive lens and a negative lens arecemented, a negative lens, and a positive lens.

The image-forming lenses of those embodiments perform focusing to alimited object distance by shifting each of the first group and thesecond group to the object side by a different extension amount, andsatisfy Conditional Expressions A, K, and L to N, as described inExamples 11 to 17 later described. And in Example 11 to 15, theimage-forming lens satisfies conditional Expressions A, K, O, P, L, M,and N.

With reference to FIGS. 35A to 35C and 36, an embodiment of a portableinformation terminal device will be explained. FIGS. 35A to 35Cillustrate external views of a camera device (a camera function part ofthe portable information terminal device), and FIG. 36 illustrates asystem constitution of the portable information terminal device. Asillustrated in FIG. 36, a portable information terminal device 30 has ashooting lens 31 and a light-receiving element (an electronic imagesensor on which 10 million to 15 million pixels are two-dimensionallyarranged) 45, and an image of a photographic subject formed by theshooting lens 31 is received by the light-receiving element 45.

As the shooting lens 31, in particular, image-forming lenses of Examples1 to 17 described later are used.

An output from the light-receiving element 45 is converted to a digitalimage by a signal processor 42 controlled by a central processing unit40. After a predetermined image processing is performed on this image inan image processor 41 controlled by the central processing unit 40, theimage is recorded on a semiconductor memory 44.

On a liquid crystal display monitor 38, a shooting image on which theimage processing is performed in the image processor 41 can bedisplayed, and an image recorded on the semiconductor memory 44 can bedisplayed. Additionally, the image recorded on the semiconductor memory44 can be sent to an external device by use of a communication card orthe like 43.

The image processor 41 also has a function of performing an electricalcorrection of shading, trimming of an image, and the like.

The shooting lens 31 is in a collapsed state when carrying, asillustrated in FIG. 35A, and when a user operates a power switch 36 andthe power is on, a lens barrel is extended as illustrated in FIG. 35B.

At this time, in the lens barrel, each group of a zoom lens is arrangedin such a manner that an object distance is infinity. And focusing to alimited object distance is performed by half-pressing of a shutterbutton 35.

Focusing is performed by shifting the first group and the second groupby a different extension amount.

In a case where the image recorded on the semiconductor memory 44 isdisplayed on the liquid crystal display monitor 38, and is sent to theexternal device by use of the communication card 43, or the like,operation is performed by an operation button 37 illustrated in FIG.35C. Each of the semiconductor memory 44, the communication card 43, andthe like is inserted in slots 39A or 39B which is exclusive orgeneral-purpose, and used. In FIGS. 35A to 35C, reference signs 32 and33 denote a flash and a viewfinder, respectively.

In a case where the shooting lens 31 is collapsed, each lens group isnot always necessary to be aligned on an optical axis. For example, thefirst group or the second group is displaced from the optical axis, andis stored in parallel with other lens group, and thereby it is possibleto further make the portable information terminal device thinner.

In the portable information terminal device having a camera device as ashooting function part as described above, image-forming lenses ofExamples 1 to 17 described later are used. Therefore, for example, it ispossible to achieve a portable information terminal device having asmall and high-picture-quality camera function using the light-receivingelement 45 on which more than 10 million pixels are arranged.

Hereinafter, ten specific examples of image-forming lenses will beexplained.

The meaning of reference signs in each example is as follows.

F: focal length of entire optical system

Fno: aperture value (f-number)

R: radius of curvature

D: surface interval

Nd: refractive index (d-line)

νd: Abbe's number

An aspheric surface is expressed by a known expression (Expression 1) byuse of a height from an optical axis: H, a shift in the optical axisdirection in the position of H: X, a constant of the cone: k, asphericcoefficients: C4, C6, C8, C10, . . . , and a paraxial radius ofcurvature: R.X=(H ² /R)/[1+{1−k(H/r)²}^(1/2) ]+C4H ⁴ +C6H ⁶ +C8H ⁸ +C10H ¹⁰+ . ..  [Expression 1]

Example 1

A lens constitution of Example 1 is illustrated in FIG. 1.

In Example 1, F=18.3 mm, and Fno=2.51.

Data of Example 1 is described in Table 1.

TABLE 1 SURFACE NUMBER R D Nd νd  1 24.64 1.0 1.6180 63.3  2 10.09 6.9 3 −17.14 0.8 1.4970 81.5  4 −50.86 0.1  5 34.34 3.9 1.8830 40.8  6−17.25 0.7 1.9229 20.9  7 −37.26 2.1  8 INF D1  9 21.98 3.6 1.8830 40.810 −16.24 0.8 1.5814 40.9 11 29.01 4.7 12 −13.81 0.7 1.9229 20.9 13−812.55 2.7 1.8830 40.8 14 −20.84 0.4 15 −259.69 2.7 1.8640 40.6  16*−31.30 D2 17 INF 2.5 1.5168 64.2 18 INF —

In Table 1, “INF” denotes “∞ (infinity)”, and “surface number with *(asterisk)” denotes “an aspheric surface”. And each of “D1” and “D2”denotes each of extension amounts of the first group and the secondgroup in accordance with focusing, respectively. Those are the same asin the following Examples.

“Aspheric Surface”

Aspheric surface data of the 16th surface is as follows.

k=−2.67

C4=−8.187E−05

C6=−7.333E−08

C8=−8.469E−09

C10=−7.192E−11

C12=−1.399E−13

C14=3.892E−15

C16=2.779E−17

C18=−3.235E−19

In the above, for example, “−3.235E−19” denotes “−3.235×10⁻¹⁹”. This isthe same as in the following.

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 2. A unit ofthe extension amounts is “mm”. Those are the same as in the followingExamples.

TABLE 2 OBJECT DISTANCE INFINITY 200 mm D1 4.4 3.9 D2 12.9 14.5

“Parameter Value of Conditional Expression”

d1₂₋₃/d1₁₋₂=0.02

|f1₁/F|=1.6

R1₂/R1₃=−0.6

f1_(n1)/f1_(n12)=1.9

f1_(ep)/f2₁₁=1.2

Nd3·νd3−Nd4·νd4=36.7

|R1₁/R2_(e)|=0.8

|R1_(e)/R2₁|=1.6

Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|−0.51

Example 2

A lens constitution of Example 2 is illustrated in FIG. 3.

In Example 2, F=18.3 mm, and Fno=2.51.

Data of Example 2 is described in Table 3.

TABLE 3 SURFACE NUMBER R D Nd νd  1 19.90 1.2 1.5891 61.2  2* 9.52 4.8 3 −20.20 0.8 1.4970 81.5  4 INF 0.1  5 24.32 3.2 1.8830 40.8  6 −19.090.8 1.8081 22.8  7 −76.21 2.2  8 INF D1  9 20.39 4.3 1.8830 40.8 10−14.29 0.8 1.5955 39.2 11 29.00 3.4 12 −13.24 0.8 1.8081 22.8 13 46.533.6 1.8830 40.8 14 −23.60 0.1 15 −144.22 2.1 1.8540 40.4  16* −26.90 D217 INF 2.5 1.5168 64.2 18 INF —“Aspheric Surface”Aspheric surface data of the second surface is as follows.

k=−0.583

C4=7.816E−05

C6=7.063E−07

C8=1.411E−08

C10=−2.787E−10

C12=4.589E−12

Aspheric surface data of the 16th surface is as follows.

k=0.000

C4=8.436E−05

C6=−1.864E−07

C8=1.048E−08

C10=−9.852E−11

C12=3.891E−13

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 4.

TABLE 4 OBJECT DISTANCE INFINITY 200 mm D1 4.4 3.98 D2 12.8 15.2“Parameter value of conditional expression”d1₂₋₃/d1₁₋₂=0.02|f1₁/F|=1.8R1₂/R1₃=−0.5f1_(n1)/f1_(n12)=1.9Nd3·νd3−Nd4·νd4=35.6f1_(ep)/f2₁₁=1.2|R1₁/R2_(e)|=0.7|R1_(e)/R2₁|=3.7Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−0.76

Example 3

A lens constitution of Example 3 is illustrated in FIG. 5.

In Example 3, F=18.3 mm, and Fno=2.56.

Data of Example 3 is described in Table 5.

TABLE 5 SURFACE NUMBER R D Nd νd  1* 30.65 1.2 1.5163 64.1  2* 9.52 6.7 3 INF 1.0 1.7400 28.3  4 41.99 0.7  5 18.53 2.5 1.8348 42.7  6 −721.822.2  7 INF D1  8 22.29 3.9 1.8348 42.7  9 −12.82 1.0 1.6034 38.0 1031.75 3.3 11 −11.50 0.9 1.8081 22.8 12 1396.54 2.5 1.8348 42.7 13 −17.070.1 14 −120.59 2.2 1.8014 45.4  15* −25.01 D2 16 INF 2.5 1.5168 64.2 17INF —“Aspheric Surface”Aspheric surface data of the first surface is as follows.

k=0.00

C4=6.848E−05

C6=−1.392E−06

C8=1.123E−08

C10=−4.372E−11

C12=6.571E−14

Aspheric surface data of the second surface is as follows.

k=−0.118

C4=7.334E−05

C6=5.982E−08

C8=−3.967E−08

C10=5.909E−10

C12=−3.021E−12

Aspheric surface data of the 15th surface is as follows.

k=0.00

C4=8.333E−05

C6=−3.402E−07

C8=1.633E−08

C10=−1.820E−10

C12=8.154E−13

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 6.

TABLE 6 OBJECT DISTANCE INFINITY 200 mm D1 3.81 3.41 D2 15.9 17.6“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.1|f1₁/F|=1.5R1₂/R1₃=0.0f1_(n1)/f1_(n12)−0.9f1_(ep)/f2₁₁=2.1|R1₁/R2_(e)|=1.2|R1₁/R2₁|=33.4Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−0.63

Example 4

A lens constitution of Example 4 is illustrated in FIG. 7.

In Example 4, F=18.3 mm, and Fno=2.56.

Data of Example 4 is described in Table 7.

TABLE 7 SURFACE NUMBER R D Nd νd  1* 22.74 1.2 1.5891 61.2  2* 9.52 6.0 3 −23.31 1.0 1.7380 32.3  4 −240.38 0.1  5 25.75 3.9 1.8348 42.7  6−36.68 2.1  7 INF D1  8 21.88 4.0 1.8348 42.7  9 −12.24 1.0 1.5927 35.310 25.79 3.2 11 −12.03 0.9 1.8081 22.8 12 −226.3 2.3 1.8348 42.7 13−16.65 0.1  14* −61.77 2.2 1.8014 45.4 15 −22.31 D2 16 INF 2.5 1.516864.2 17 INF —“Aspheric Surface”Aspheric surface data of the first surface is as follows.

k=3.782

C4=2.119E−04

C6=−3.985E−06

C8=3.189E−08

C10=−1.666E−10

Aspheric surface data of the second surface is as follows.

k=0.235

C4=2.716E−04

C6=−2.065E−06

C8=−3.073E−08

C10=8.787E−10

C12=−9.428E−12

Aspheric surface data of the 14th surface is as follows.

k=0.00

C4=−9.174E−05

C6=9.423E−08

C8=−1.110E−08

C10=1.830E−10

C12=−3.459E−12

C14=3.667E−14

C16=−1.729E−16

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 8.

TABLE 8 OBJECT DISTANCE INFINITY 200 mm D1 3.93 3.41 D2 13.9 17.6“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.02|f1₁/F|=1.6R1₂/R1₃=−0.4f1_(n1)/f1_(n12)=2.0f1_(ep)/f2₁₁=1.9|R1₁/R2_(e)|=1.0|R1_(e)/R2₁|=1.7Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−0.85

Example 5

A lens constitution of Example 5 is illustrated in FIG. 9.

In Example 5, F=18.3 mm, and Fno=2.53.

Data of Example 5 is described in Table 9.

TABLE 9 SURFACE NUMBER R D Nd νd  1 19.77 0.9 1.6180 63.3  2 8.60 5.6  3−20.41 0.8 1.4970 81.5  4 −150.02 0.1  5 17.79 2.9 1.8830 40.8  6 −19.190.8 1.9229 20.9  7 −58.99 2.1  8 INF D1  9 21.71 3.0 1.8830 40.8 10−13.58 0.8 1.5814 40.9 11 19.03 4.1 12 −8.05 0.8 1.9229 20.9 13 −22.780.1 14 247.87 4.0 1.8160 46.6 15 −13.61 0.1  16* −43.62 1.9 1.8513 40.117 −29.20 D2 18 INF 2.5 1.5168 64.2 19 INF —“Aspheric Surface”Aspheric surface data of the 16th surface is as follows.

k=0.00

C4=−9.824E−05

C6=−2.028E−07

C8=−1.981E−09

C10=2.483E−12

C12=−1.441E−13

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 10.

TABLE 10 OBJECT DISTANCE INFINITY 200 mm D1 3.44 3.14 D2 12.38 14.04“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.02|f1₁/F|=1.4R1₂/R1₃=−0.4f1_(n1)/f1_(n12)=1.6Nd3·νd3−Nd4·νd4=36.7f1_(ep)/f2₁₁=1.1|R1₁/R2_(e)|=0.7|R1_(e)/R2₁|=2.7Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−0.74

Example 6

A lens constitution of Example 6 is illustrated in FIG. 11.

In Example 6, F=16.5 mm, and Fno=2.64.

Data of Example 6 is described in Table 11.

TABLE 11 SURFACE NUMBER R D Nd νd  1 16.37 0.9  1.4875 70.2  2* 7.386.19  3 −17.41 1.09 1.7200 43.7  4 −71.59 0.10  5 27.50 2.82 1.8830 40.8 6 −18.41 0.16  7 −16.65 0.80 1.8467 23.8  8 −30.89 2.15  9 INF D1 1019.96 3.54 1.8830 40.8 11 −22.52 0.10 12 −36.72 0.80 1.5927 35.3 1325.84 2.88 14 −13.25 0.80 1.8467 23.8 15 33.34 3.30 1.8830 40.8 16−28.69 0.10 17 −856.38 2.32 1.8640 40.6  18* −25.13 D2 19 INF 2.5 1.5168 64.2 20 INF —“Aspheric Surface”Aspheric surface data of the second surface is as follows.

k=−0.562

C4=9.683E−05

C6=1.527E−06

C8=9.114E−09

C10=2.182E−11

C12=4.684E−12

Aspheric surface data of the 18th surface is as follows.

k=1.983

C4=1.140E−04

C6=−2.788E−07

C8=1.672E−08

C10=−2.084E−10

C12=9.983E−13

C14=4.464E−15

C16=−6.342E−17

C18=1.700E−19

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 12.

TABLE 12 OBJECT DISTANCE INFINITY 200 mm D1 4.99 4.64 D2 13.3 14.4“Parameter value of conditional expression”d1₂₋₃/d1₁₋₂=0.02|f1₁/F|=1.7R1₂/R1₃=−0.4f1_(n1)/f1_(n12)=2.1f1_(ep)/f2₁₁=1.0|R1₁/R2₁|=0.7|R1_(e)/R2₁|=1.6Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−0.50

Example 7

A lens constitution of Example 7 is illustrated in FIG. 13.

In Example 7, F=17.5 mm, and Fno=2.55.

Data of Example 7 is described in Table 13.

TABLE 13 SURFACE NUMBER R D Nd νd  1 17.74 0.9 1.4875 70.2  2* 8.08 5.4 3 −18.54 0.8 1.7200 43.7  4 −121.68 0.1  5 25.25 3.0 1.8830 40.8  6−19.77 0.2  7 −17.74 0.8 1.8467 23.8  8 −32.72 2.2  9 INF D1 10 20.504.3 1.8830 40.8 11 −13.27 0.8 1.6129 37.0 12 32.41 3.2 13 −12.68 0.81.8467 23.8 14 48.44 3.4 1.8830 40.8 15 −22.19 0.1 16 −166.28 2.1 1.854040.4  17* −26.30 D2 18 INF 2.5 1.5168 64.2 19 INF —“Aspheric Surface”Aspheric surface data of the second surface is as follows.

k=−0.347

C4=4.050E−05

C6=8.163E−07

C8=−6.620E−10

C10=2.008E−10

Aspheric surface data of the 17th surface is as follows.

k=0.00

C4=8.836E−05

C6=−1.803E−07

C8=1.093E−08

C10=−1.094E−10

C12=4.348E−13

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 14.

TABLE 14 OBJECT DISTANCE INFINITY 200 mm D1 4.44 4.06 D2 13.07 14.29“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.02|f1₁/F|=1.8R1₂/R1₃=−0.4f1_(n1)/f1_(n12)=2.2f1_(ep)/f2₁₁=1.3|R1₁/R2_(e)|=0.7|R1_(e)/R2₁|=1.8Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−0.51

Example 8

A lens constitution of Example 8 is illustrated in FIG. 15.

In Example 8, F=19.0 mm, and Fno=2.54.

Data of Example 8 is described in Table 15.

TABLE 15 SURFACE NUMBER R D Nd νd 1 20.47 0.9 1.6180 63.3 2 9.06 5.2 3−23.31 0.8 1.4970 81.5 4 519.78 0.2 5 18.55 3.7 1.8830 40.8 6 −20.43 0.81.9229 20.9 7 −70.46 2.1 8 INF D1 9 20.74 3.0 1.8830 40.8 10  −14.66 0.81.5814 40.9 11  19.75 4.1 12  −9.23 0.8 1.9229 20.9 13  −23.60 0.1 14 −379.22 3.3 1.8160 46.6 15  −16.67 0.1 16  −51.28 2.1 1.8513 40.1 17*−28.81 D2 18  INF 2.5 1.5168 64.2 19  INF —“Aspheric Surface”Aspheric surface data of the 17th surface is as follows.

k=0.00

C4=6.978E−05

C6=1.618E−07

C8=4.033E−10

C10=−1.563E−12

C12=9.243E−15

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 16.

TABLE 16 OBJECT DISTANCE INFINITY 200 mm D1 4.3 3.9 D2 14.17 16.12“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.04|f1₁/F|=1.4R1₂/R1₃=−0.4f1_(n1)/f1_(n12)=1.7f1_(ep)/f2₁₁=1.1Nd3·νd3−Nd4˜νd4=36.7|R1₁/R2_(e)|=0.7|R1_(e)/R2₁|=3.4Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−0.69

Example 9

A lens constitution of Example 9 is illustrated in FIG. 17.

In Example 9, F=20.3 mm, and Fno=2.55.

Data of Example 9 is described in Table 17.

TABLE 17 SURFACE NUMBER R D Nd νd  1 19.42 0.9 1.6188 63.9  2* 10.31 4.8 3 −19.37 0.8 1.4970 81.5  4 1198.3 0.1  5 25.45 3.5 1.8830 40.8  6−15.48 0.8 1.8467 23.8  7 −50.44 1.8  8 INF D1  9 21.94 4.1 1.8830 40.810 −15.09 0.8 1.5814 40.7 11 24.97 3.6 12 −12.79 0.8 1.8467 23.8 1362.89 3.5 1.8830 40.8 14 −21.04 0.1 15 −95.87 2.1 1.8540 40.4  16*−26.38 D2 17 INF 2.5 1.5168 64.2 18 INF —“Aspheric Surface”Aspheric surface data of the second surface is as follows.

k=0.395

C4=−4.702E−05

C6=7.378E−07

C8=−4.847E−08

C10=8.724E−10

C12=−7.929E−12

Aspheric surface data of the 16th surface is as follows.

k=0.00

C4=7.896E−05

C6=−1.450E−06

C8=7.390E−08

C10=−1.951E−09

C12=3.221E−11

14=−3.238E−13

C16=1.815E−15

C18=−4.343E−18

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 18.

TABLE 18 OBJECT DISTANCE INFINITY 200 mm D1 4.39 3.99 D2 13.94 15.6“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.02|f1₁/F|=1.8R1₂/R1₃=−0.5f1_(n1)/f1_(n12)=2.0f1_(ep)/f2₁₁=1.1Nd3·νd3−Nd4·νd4=32.9|R1₁/R2_(e)|=0.7|R1_(e)/R2₁|=2.3Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−0.62

Example 10

A lens constitution of Example 10 is illustrated in FIG. 19.

In Example 10, F=19.0 mm, and Fno=2.53.

Data of Example 10 is described in Table 19.

TABLE 19 SURFACE NUMBER R D Nd νd 1 20.04 0.8 1.6188 63.9  2* 9.52 6.8 3−21.04 1.0 1.6727 32.1 4 −64.44 0.1 5 30.67 2.5 1.8160 46.6 6 −40.21 2.17 INF D1 8 22.42 4.1 1.8830 40.8 9 −13.96 1.0 1.6259 35.7 10  26.17 3.311  −13.72 0.9 1.8081 22.8 12  93.61 2.6 1.8348 42.7 13  −19.29 0.1 14 −83.67 2.0 1.8061 40.9 15* −26.05 D2 16  INF 2.5 1.5168 64.2 17  INF —“Aspheric Surface”Aspheric surface data of the second surface is as follows.

k=−0.586

C4=7.104E−05

C6=8.861E−07

C8=2.716E−09

C10=−7.117E−11

C12=2.029E−12

Aspheric surface data of the 15th surface is as follows.

k=0.00

C4=7.987E−05

C6=−3.354E−07

C8=1.750E−08

C10=−2.011E−10

C12=9.573E−13

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 20.

TABLE 20 OBJECT DISTANCE INFINITY 200 mm D1 4.18 3.66 D2 16.3 18.1“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.02|f1₁/F|=1.5R1₂/R1₃=−0.5f1_(n1)/f1_(n12)=1.8f1_(ep)/f2₁₁=2.1|R1₁/R2_(e)|=0.8|R1_(e)/R2₁|=1.8Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−0.54

FIGS. 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 are aberration diagramsregarding Examples 1 to 10. In the above diagrams, “d” denotes a d-line,“g” denotes a g-line. In an astigmatism diagram, a solid line “Sag”denotes astigmatism in a sagittal plane, and a dashed line “Mer” denotesastigmatism in a meridional plane. In a spherical aberration diagram, adashed line denotes “a sine condition”.

As is clear from those aberration diagrams, in each example, the lenshas excellent performance. In each Example, aberration of the lens iscorrected at high level. That is, spherical aberration, astigmatism,field curvature, and transverse chromatic aberration are sufficientlycorrected, and an absolute value of distortion becomes less than orequal to 2.0%. In addition, it is possible to be a wide field angle inwhich a half-field angle is equal to or more than 38 degrees (Examples 1to 7). Moreover, the lens is bright, in which the f-number is 2.51 to2.64, and has a large diameter, and ensures suitable imagingperformance.

The image-forming lens of each Example is a bright lens as describedabove, and preferably satisfies Conditional Expression J, and thereforeit is possible to perform focusing in a short time. Accordingly, it ispossible to perform high-speed shooting.

Each of the image-forming lenses of Examples 1 to 10 is an image-forminglens that has suitable performance, in which a reference closest imagingdistance is set to 200 mm and enables to perform near-distance shootingwith respect to a photographic subject.

Hereinafter, seven another specific examples of image-forming lenseswill be explained.

Example 11

A lens constitution of Example 11 is illustrated in FIG. 21.

In Example 11, F=18.3 mm, and Fno=2.56.

Data of Example 11 is described in Table 21.

TABLE 21 SURFACE NUMBER R D Nd νd  1 23.72 1.1 1.6516 58.6  2 9.52 3.4 3* 59.04 1.7 1.8061 40.4  4 −90.61 1.1  5 −18.02 0.9 1.6129 37.0  613.37 3.0 1.8348 42.7  7 −29.58 2.2  8 INF D1  9 21.55 4.3 1.8348 42.710 −13.34 0.8 1.5750 41.5 11 31.58 2.9 12 −16.16 0.8 1.8467 23.8 1331.25 3.9 1.8348 42.7 14 −19.67 0.1 15* −181.46 2   1.8540 40.4 16−41.88 D2 17 INF 2.5 1.5168 64.2 18 INF —“Aspheric Surface”Aspheric surface data of the third surface is as follows.

k=16.511

C4=1.057E−05

C6=−8.295E−07

C8=3.194E−08

C10=−4.098E−10

C12=−1.550E−12

C14=7.232E−14

C16=−6.999E−16

C18=−5.662E−18

Aspheric surface data of the 15th surface is as follows.

k=0.000

C4=−9.157E−05

C6=1.096E−06

C8=−5.305E−08

C10=1.237E−09

C12=−1.839E−11

C14=1.517E−13

C16=−5.705E−16

C18=3.284E−19

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 22.

TABLE 22 OBJECT DISTANCE INFINITY 200 mm D1 4.46 3.85 D2 14.10 15.78“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.32f1₁/f1₂=−0.57f1_(e)/f2₁=3.24(Nd4·νd4−Nd3·νd3)/(Nd5·νd5−Nd6·νd6)=1.44|R1₁/R2_(e)|=0.57|R1_(e)/R2₁|=1.37Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−4.4E−1

Example 12

A lens constitution of Example 12 is illustrated in FIG. 23.

In Example 12, F=18.3 mm, and Fno=2.51.

Data of Example 12 is described in Table 23.

TABLE 23 SURFACE NUMBER R D Nd νd  1 32.70 1.0 1.6030 65.4  2 10.37 4.7 3 32.38 2.0 1.8830 40.8  4 433.33 1.3  5 −30.73 0.8 1.5927 35.3  611.06 4.0 1.8830 40.8  7 −50.78 2.1  8 INF D1  9 21.19 4.0 1.8830 40.810 −13.84 0.8 1.7174 29.5 11 18.12 4.0 12* −9.92 0.8 1.9068 21.2 13*−17.66 0.1 14 −1601.33 5.5 1.8830 40.8 15 −15.00 D2 16 INF 2.5 1.516864.2 17 INF —“Aspheric Surface”Aspheric surface data of the 12th surface is as follows.

k=0.000

C4=1.702E−05

C6=8.936E−07

Aspheric surface data of the 13th surface is as follows.

k=−2.424

C4=1.035E−04

C6=1.196E−06

C8=1.421E−09

C10=−1.023E−10

C12=3.055E−13

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 24.

TABLE 24 OBJECT DISTANCE INFINITY 200 mm D1 2.72 2.34 D2 11.60 13.29“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.64f1₁/f1₂=−0.46f1_(e)/f2₁=2.51(Nd4·νd4−Nd3·νd3)/(Nd5·νd5−Nd6·νd6)=0.79|R1₁/R2_(e)|=0.90|R1_(e)/R2₁|=2.40Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−6.5E−1

Example 13

A lens constitution of Example 13 is illustrated in FIG. 25.

In Example 13, F=18.3 mm, and Fno=2.56.

Data of Example 13 is described in Table 25.

TABLE 25 SURFACE NUMBER R D Nd νd  1* 23.77 1.1 1.5163 64.1  2* 9.53 4.9 3 32.35 1.7 1.8830 40.8  4 133.80 1.7  5 −17.05 0.9 1.6200 36.3  617.77 3.0 1.8830 40.8  7 −29.70 2.2  8 INF D1  9 22.92 4.2 1.8830 40.810 −11.87 0.8 1.6727 32.2 11 30.47 2.9 12 −15.38 0.8 1.8467 23.9 13−129.05 0.1 14 72.46 3.8 1.8014 45.4 15* −16.82 D2 16 INF 2.5 1.516864.2 17 INF —“Aspheric Surface”Aspheric surface data of the first surface is as follows.

k=−5.163

C4=1.990E−04

C6=−3.715E−06

C8=5.008E−08

C10=−3.466E−10

C12=1.083E−12

Aspheric surface data of the second surface is as follows.

k=0.1880

C4=1.317E−04

C6=−5.317E−06

C8=6.213E−08

C10=−6.522E−10

C12=1.333E−12

C14=1.496E−13

C16=−3.280E−15

C18=1.898E−17

Aspheric surface data of the 15th surface is as follows.

k=0.4582

C4=1.119E−04

C6=2.677E−07

C8=6.947E−09

C10=−9.656E−11

C12=4.708E−13

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 26.

TABLE 26 OBJECT DISTANCE INFINITY 200 mm D1 5.58 5.06 D2 14.26 15.92“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.36f1₁/f1₂=−0.66 f1_(e)/f2₁=3.48 (Nd4·νd4−Nd3·νd3)/(Nd5·νd5−Nd6·νd6)=0.78|R1₁/R2_(e)|=1.41|R1_(e)/R2₁|=1.30Log|(D1_(∞)−D1₁)/(D2_(∞)−D2_(t))|=−5.0E−1

Example 14

A lens constitution of Example 14 is illustrated in FIG. 27.

In Example 14, F=18.3 mm, and Fno=2.56.

Data of Example 14 is described in Table 27.

TABLE 27 SURFACE NUMBER R D Nd νd  1 23.74 1.0 1.4875 70.2  2* 8.45 3.1 3 20.93 1.2 1.8503 32.3  4 39.97 2.0  5 −25.35 1.3 1.4970 81.5  6−18.50 0.1  7 −18.19 0.9 1.6398 34.5  8 14.61 2.6 1.8830 40.8  9 −38.522.2 10 INF D1 11 22.62 4.0 1.8830 40.8 12 −16.98 0.8 1.6129 37.0 1331.37 2.6 14 −22.16 0.8 1.8467 23.8 15 32.82 3.4 1.8348 42.7 16 −28.490.1 17 −91.68 2.0 1.8540 40.4 18* −27.85 D2 19 INF 2.5 1.5168 64.2 20INF —“Aspheric Surface”Aspheric surface data of the second surface is as follows.

k=−0.1284

C4=2.211E−05

C6=−9.313E−07

C8=1.637E−08

C10=−2.689E−10

Aspheric surface data of the 18th surface is as follows.

k=−27.846

C4=−6.811E−05

C6=1.598E−06

C8=−1.011E−08

C10=3.747E−11

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 28.

TABLE 28 OBJECT DISTANCE INFINITY 200 mm D1 5.03 4.92 D2 14.50 15.18“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.64f1₁/f1₂=−0.55f1_(e)/f2₁=6.32(Nd4·νd4·Nd3·νd3)/(Nd5·νd5−Nd6·νd6)=1.19|R1₁/R2_(e)|=0.85|R1_(e)/R2₁|=1.70Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−7.9E−1

Example 15

A lens constitution of Example 15 is illustrated in FIG. 29.

In Example 15, F=18.3 mm, and Fno=2.54.

Data of Example 15 is described in Table 29.

TABLE 29 SURFACE NUMBER R D Nd νd  1 32.81 1.0 1.4875 70.2  2* 8.59 3.2 3 25.44 1.5 1.6259 35.7  4 36.81 0.1  5 21.62 1.5 1.5174 52.4  6 59.191.4  7 −20.20 0.9 1.6398 34.5  8 16.33 2.6 1.8830 40.8  9 −30.60 2.2 10INF D1 11 23.00 4.0 1.8830 40.8 12 −15.98 0.8 1.6129 37.0 13 32.12 2.614 −20.80 0.8 1.8467 23.8 15 31.58 3.4 1.8348 42.7 16 −28.00 0.1 17−75.33 2 1.8540 40.4 18* −26.27 D2 19 INF 2.5 1.5168 64.2 20 INF —“Aspheric Surface”

Aspheric surface data of the second surface is as follows.

k=−0.2533

C4=−2.254E−05

C6=4.226E−07

C8=−1.066E−08

C10=6.961E−11

Aspheric surface data of the 18th surface is as follows.

k=−24.622

C4=−8.962E−05

C6=1.920E−06

C8=−1.294E−08

C10=4.865E−11

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 30.

TABLE 30 OBJECT DISTANCE INFINITY 200 mm D1 4.97 4.86 D2 14.95 16.49“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.03f1₁/f1₂=−0.19f1_(e)/f2₁=2.73(Nd4·νd4−Nd3·νd3)/(Nd5·νd5−Nd6·νd6)=1.19|R1₁/R2_(e)|=1.25|R1_(e)/R2₁|=1.33Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−1.2E+1

Example 16

A lens constitution of Example 16 is illustrated in FIG. 31.

In Example 16, F=18.3 mm, and Fno=2.54.

Data of Example 16 is described in Table 31.

TABLE 31 SURFACE NUMBER R D Nd νd  1* 24.17 1.1 1.5163 64.1  2* 9.52 4.7 3 28.33 1.7 1.8830 40.8  4 86.37 1.8  5 −18.31 0.9 1.6200 36.3  6 23.000.1  7 21.57 3.0 1.8830 40.8  8 −33.72 2.2  9 INF D1 10 20.85 4.2 1.883040.8 11 −11.73 0.8 1.6727 32.2 12 27.00 3.0 13 −14.17 0.8 1.8467 23.9 14−88.00 0.1 15 70.40 3.8 1.8014 45.4 16* −16.50 D2 17 INF 2.5 1.5168 64.218 INF —“Aspheric Surface”Aspheric surface data of the first surface is as follows.

k=−4.6053

C4=1.969E−04

C6=−3.766E−06

C8=5.015E−08

C10=−3.432E−10

C12=1.049E−12

Aspheric surface data of the second surface is as follows.

k=0.1696

C4=1.384E−04

C6=−5.402E−06

C8=6.167E−08

C10=−6.439E−10

C12=1.450E−12

C14=1.468E−13

C16=−3.256E−15

C18=1.874E−17

Aspheric surface data of the 16th surface is as follows.

k=0.3774

C4=1.174E−04

C6=3.790E−07

C8=5.500E−09

C10=−8.152E−11

C12=4.137E−13

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 32.

TABLE 32 OBJECT DISTANCE INFINITY 200 mm D1 5.44 4.93 D2 14.38 15.99“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.38f1₁/f1₂=−0.66|R1₁/R2_(e)|=1.46|R1_(e)/R2₁|=1.62Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−5.0E−1

Example 17

A lens constitution of Example 17 is illustrated in FIG. 33.

In Example 17, F=18.3 mm, and Fno=2.54.

Data of Example 17 is described in Table 33.

TABLE 33 SURFACE NUMBER R D Nd νd  1* 31.11 0.9 1.5891 61.2  2* 9.52 3.7 3 32.00 1.8 1.8830 40.8  4 136.59 3.4  5 −19.48 0.7 1.6989 30.1  6165.05 0.1  7 35.25 2.7 1.8830 40.8  8 −25.61 2.2  9 INF D1 10 19.71 3.91.8830 40.8 11 −12.32 0.7 1.6727 32.2 12 20.23 3.5 13 −12.16 0.8 1.846723.9 14 −40.98 0.1 15 105.45 3.6 1.8014 45.4 16* −16.04 D2 17 INF 2.51.5168 64.2 18 INF —“Aspheric Surface”Aspheric surface data of the first surface is as follows.

k=0.000

C4=2.745E−05

C6=−1.449E−06

C8=1.891E−08

C10=−1.165E−10

C12=2.814E−13

Aspheric surface data of the second surface is as follows.

k=−0.4204

C4=7.192E−05

C6=−2.089E−06

C8=4.543E−08

C10=−9.522E−10

C12=1.209E−11

C14=3.593E−14

C16=−2.150E−15

C18=1.340E−17

Aspheric surface data of the 16th surface is as follows.

k=−0.1779

C4=1.026E−04

C6=1.606E−07

C8=7.347E−09

C10=−9.187E−11

C12=4.297E−13

“Extension Amount”

Extension amounts of each of the first group and the second group inaccordance with focusing: D1 and D2 are described in Table 34.

TABLE 34 OBJECT DISTANCE INFINITY 200 mm D1 5.92 5.37 D2 14.94 15.61“Parameter Value of Conditional Expression”d1₂₋₃/d1₁₋₂=0.91f1₁/f1₂=−0.50|R1₁/R2_(e)|=1.94|R1_(e)/R2₁|=1.30Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|=−1.2E−1

FIGS. 22, 24, 26, 28, 30, 32, and 34 are aberration diagrams regardingExamples 11 to 17.

As described above, in the above diagrams, “d” denotes a d-line, and “g”denotes a g-line. In an astigmatism diagram, a solid line “Sag” denotesastigmatism in a sagittal plane, and a dashed line “Mer” denotesastigmatism in a meridional plane. In a spherical aberration diagram, adashed line denotes “a sine condition”.

As is clear from those aberration diagrams, in each example, the lenshas excellent performance. In each example, aberration of the lens iscorrected at high level. That is, spherical aberration, astigmatism,field curvature, and transverse chromatic aberration are sufficientlycorrected, and an absolute value of distortion becomes less than orequal to 2.0%. In addition, it is possible to be a wide field angle inwhich a half-field angle is equal to or more than 38 degrees. Moreover,the lens is bright, in which the f-number is about 2.5, and has a largediameter, and ensures suitable imaging performance.

The image-forming lens of each Example is a bright lens as describedabove, and preferably satisfies Conditional Expression N, and thereforeit is possible to perform focusing in a short time. Accordingly, it ispossible to perform high-speed shooting.

Each of the image-forming lenses of Examples 11 to 17 is animage-forming lens that has suitable performance, in which a referenceclosest imaging distance is set to 200 mm and enables to performnear-distance shooting with respect to a photographic subject.

By use of the image-forming lens system providing good performanceaccording to the examples of the present invention, even in a case wherean image sensor which has a large imaging plane and a large number ofpixels is used, there is no need to increase the size of an imagingapparatus.

By using the image-forming lenses having excellent performance accordingto the examples of the present invention, in a case where an imagesensor in which the size of an imaging plane is large and the number ofpixels is large is used, there is no need to make an imaging apparatuslarger.

As described above, according to the examples of the present invention,it is possible to provide an image-forming lens having two positive andpositive groups that achieves good performance and miniaturization. Inaddition, according to the examples of the present invention, it ispossible for the image-forming lens to be a wide field angle in which ahalf-field angle is 35.6 degrees to 41 degrees, and to be bright inwhich the f-number is 2.51 to 2.64, and to provide good performance.

Accordingly, by using the image-forming lens as a shooting lens, it ispossible to achieve a camera device and a portable information terminaldevice providing excellent performance.

Additionally, in each example, with respect to a 10-million-pixel imagesensor having a rectangular imaging plane a diagonal length of which is28.6 mm, it is possible to obtain a small imaging apparatus where theentire optical length (a distance between a lens surface on a mostobject side of the image-forming lens and the imaging plane) isapproximately 1.7 times (infinity focus state).

Note that the reference closest imaging distance is a closest imagingdistance where imaging is possible, in terms of an aberrationcorrection, in a state of maintaining an optical performance in design.Accordingly, the reference closest imaging distance is determined as adesign condition. However, in fact, if imaging is performed in adistance closer than the reference closest imaging distance, apractically sufficient imaging is possible.

In the examples, the reference closest imaging distance is set to 200mm.

Although the present invention has been described in terms of exemplaryembodiments, it is not limited thereto. It should be appreciated thatvariations may be made in the embodiments described by persons skilledin the art without departing from the scope of the present invention asdefined by the following claims.

The invention claimed is:
 1. An image forming lens comprising, in anorder from an object side to an image side: a first group with apositive refractive power; an aperture stop; and a second group with apositive refractive power, wherein each of the first group and thesecond group shifts independently to perform focusing to a limitedobject distance, the first group includes, in order from the objectside, a negative lens and a positive lens, a lens disposed on the mostobject side in the first group is a negative meniscus lens a convexsurface of which faces the object side, the second group includes fiveor less lenses including at least one cemented lens of a positive lensand a negative lens, a negative lens, and a positive lens, both a lenssurface on the most image side in the first group and a lens surface onthe most object side in the second group have convex surfaces, and afocal length (f1₁) of the negative meniscus lens disposed on the mostobject side, and a focal length (f1₂) of a positive lens disposed on theimage side next to the negative meniscus lens satisfy a followingConditional Expression (2): −0.1>f1₁/f1₂>−1.0.
 2. The image forming lensaccording to claim 1, wherein the first group consists of five or lesslenses including two negative lenses and two or more positive lenses. 3.The image forming lens according to claim 1, wherein an air interval(d1₁₋₂) in the first group between the negative meniscus lens disposedon the most object side and the positive lens disposed on the image sidenext to the negative meniscus lens, and an air interval (d1₂₋₃) betweenthe positive lens disposed on the second from the object side in thefirst group and a lens disposed on the image side next to the positivelens satisfy a following Conditional Expression (1):0.0<d1₂₋₃/d1₁₋₂<1.0.
 4. The image forming lens according to claim 1,wherein a curvature radius (R1₁) on a surface on the object side of thenegative meniscus lens disposed on the most object side in the firstgroup, and a curvature radius (R2_(e)) on a surface on the image side ofa lens disposed on the most image side in the second group satisfy afollowing Conditional Expression (5): 0.4<|R1₁/R2_(e)|<2.1.
 5. The imageforming lens according to claim 1, wherein a curvature radius (R1_(e))on a surface on the image side of a lens disposed on the most image sidein the first group, and a curvature radius (R2₁) on a surface on theobject side of a lens disposed on the most object side in the secondgroup satisfy a following Conditional Expression (6):1.2<|R1_(e)/R2₁<2.6.
 6. The image forming lens according to claim 1,wherein a lens interval (D1_(∞)) between the first group and the secondgroup in a case where an object position is infinity, a lens interval(D1_(t)) between the first group and the second group in a case offocusing to a reference closest imaging distance, an interval (D2_(∞))between the second group and an image in a case where the objectposition is infinity, and an interval (D2_(t)) between the second groupand the image position in a case of focusing to the reference closestimaging distance satisfy a following Conditional Expression (7):−1.5E+1<Log|(D1_(∞)−D1_(t))/(D2_(∞)−D2_(t))|<−5.0E−2, where Log is takenas a common logarithm.
 7. The image forming lens according to claim 1,wherein a lens disposed on the most image side is a cemented lens of apositive lens and a negative lens, a lens disposed on the most objectside is a cemented lens of a positive lens and a negative lens, and afocal length (f1_(e)) of the cemented lens disposed on the most imageside in the first group, and a focal length (f2₁) of the cemented lensdisposed on the most object side in the second group satisfy a followingConditional Expression (3): 2.0<f1_(e)/f2₁<7.9.
 8. The image forminglens according to claim 1, where refractive index (Nd3) of a d-line of anegative lens of a cemented lens disposed on the most image side in thefirst group, an Abbe's number (νd3) of the d-line of the negative lensof the cemented lens in the first group, a refractive index (Nd4) of thed-line of a positive lens of the cemented lens disposed on the mostimage side in the first group, an Abbe's number (νd4) of the d-line ofthe positive lens of the cemented lens disposed on the most image sidein the first group, a refractive index (Nd5) of the of a positive lensof a cemented lens disposed on the most object side in the second group,an Abbe's number (νd5) of the d-line of the positive lens of thecemented lens disposed on the most object side in the second group, arefractive index (Nd6) of the d-line of a negative lens of the cementedlens disposed on the most object side in the second group, and an Abbe'snumber (νd6) of the d-line of the negative lens of the cemented lensdisposed on the most object side in the second group satisfy ConditionalExpression (4): 0.7<(Nd4·νd4−Nd3·νd3)/(Nd5·νd5−Nd6·νd6)<1.6.
 9. A cameradevice comprising the image forming lens according to claim 1 as ashooting optical system.
 10. A portable information terminal devicecomprising the camera device according to claim 9 as a camera functionpart.